WebRTCCertificateGenerator should not use std::string.

content/renderer/media/rtc_certificate.cc

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/rtc_certificate.h"
 
 #include "base/memory/ptr_util.h"
 #include "url/gurl.h"
 
 namespace content {
@@ skipping 10 matching lines @@
 std::unique_ptr<blink::WebRTCCertificate> RTCCertificate::shallowCopy() const {
   return base::WrapUnique(new RTCCertificate(certificate_));
 }
 
 uint64_t RTCCertificate::expires() const {
   return certificate_->Expires();
 }
 
 blink::WebRTCCertificatePEM RTCCertificate::toPEM() const {
   rtc::RTCCertificatePEM pem = certificate_->ToPEM();
-  return blink::WebRTCCertificatePEM(pem.private_key(), pem.certificate());
+  return blink::WebRTCCertificatePEM(
+      blink::WebString::fromUTF8(pem.private_key()),
+          blink::WebString::fromUTF8(pem.certificate()));
 }
 
 bool RTCCertificate::equals(const blink::WebRTCCertificate& other) const {
   return *certificate_ ==
          *static_cast<const RTCCertificate&>(other).certificate_;
 }
 
 const rtc::scoped_refptr<rtc::RTCCertificate>&
 RTCCertificate::rtcCertificate() const {
   return certificate_;
 }
 
 }  // namespace content